1. Field of the Invention
The present invention relates to a novolak type phenol resin, in particular to a novolak type phenol resin for resists suitable for use in forming resist patterns.
This application is based on Japanese Patent Application No. Hei 11-158798, the contents of which are incorporated herein by reference.
2. Background Art
With the recent high degree of integration of integrated circuits, pattern formation at quarter micron levels has been desired. As a means for achieving downsizing of patterns, mention may be made of a method for shortening the wavelength of the light used. As such, in particular, use of a KrF excimer laser has enabled production of 64M DRAMs and 256M DRAMs and hence has been paid much attention.
Under the circumstances, there has been an increasing demand for resist materials for high resolution lithography and a resist material that shows good pattern formation ability and has improved heat resistance, resolution and sensitivity has been keenly desired.
In accordance with the downsizing of patterns, there has been a shift in the etching process of wafers from wet etching to dry etching. As a result resists are required such that the heat upon dry etching does not deform their patterns, and hence improvement in the heat resistance of resists has been demanded.
Resists must be transparent to the above light source, so mainly polyvinylphenols have been used. However, they are insufficient in pattern shape, resolution, developability, and film retention properties and modification of polyvinylphenols has heretofore been performed. Modification of polyvinylphenols by hydrogenation and modification by various types of copolymerization with styrene monomers, acrylic monomers, etc. have been carried out to promote functionalization of polyvinylphenols. However, in pattern formation at sub-quarter-micron levels, there has been found no resist material that simultaneously satisfies the requirements for good pattern shape, resolution, sensitivity, developability, film retention properties, and heat resistance.